The monitoring of a ball grinding mill or equivalent through electrical signals derived from the mill in operation has long been known. Representative of typical monitoring systems are those shown in U.S. Pat. Nos. 2,405,059--V. Sahmel, July 3, 1946; 2,766,941--D. Weston, Oct. 16, 1956; 3,944,146--H. Stockmann et al., Mar. 16, 1976; and 4,026,479--R. Bradburn et al., May 31, 1977.
Each of these systems depend upon sound signals derived from the mill operation. However, sound signals are neither pure nor primary signals and lead to complex means for analysis and selection of different operating characteristics It is easily recognizable that a sound frequency, magnitude or characteristic pattern will change considerably over changes in loading, speed and material constituency, size and characteristics. Also in the mill environment there are extraneous sounds which will affect such systems. Therefore for operation where significant ranges of materials and different ball mill conditions exist, a sound operated system tends to be restricted to sensing a particular limited condition in a particular mill to which it is custom tailored. It is therefore desirable to establish signals more universally significant and less susceptible to error from extraneous causes.
Furthermore, the sound derived signals which are tailored to specific mill conditions are significantly altered by the physical nature of the materials being processed. Thus, for example, if a chemical additive to the raw materials affects the physical behavior of the materials enough to improve the mill throughput efficiency, it also affects the sound. Thus, preselected patterns of sound signals may not properly detect material differences in throughput efficiency which should be monitored and controlled.
There are also other shortcomings of the prior art systems and methods because the nature of the mill operation is not understood or has not been adopted as an integral part of the monitoring and control methods. Thus, for example, a number of interrelated variables may effect efficiency, such as the amount of charge of materials in the mill, the charge characteristics including the chemical additives used, and the ball grinding efficiency. Nevertheless, most systems and methods are responsive only to single control factors such as the rate of flow of materials through the mill without regard to the grinding efficiency, which could change drastically in characteristic depending upon other mill conditions. It is therefore desirable to employ control signals representative of complex interactions in the mill yet indicative of the true throughput efficiency of a uniform product.
Also it is desirable to have methods and signals available for both instantaneous on-line and long term analysis of mill conditions. Few control methods or systems afford a compatible dual capability of this sort.
Particularly for use under semi-automatic operation with operator intervention or operator analysis of mill conditions in set up maintenance or control functions, it becomes necessary to communicate mill conditions in a way that cannot be misinterpreted, or misunderstood or overlooked. In this respect any signals or displays which make an operator depend upon the visual sensing of a particu1ar value of a variable signal magnitude or meter reading, tend to cause operator error, particularly where operators may not have significant mill operation analysis skills.
Accordingly, it is a general objective of this invention to improve the prior art methods of deriving signals, displays and operational controls of grinding mills. Throughout the following description, drawings and claims further objectives, advantages and features of the invention will be set forth.